The present invention generally relates to keyswitches as well as keyboards using keyswitches, and more particularly to a low height keyswitch for use in keyboards of compact, portable computers.
FIGS. 1A and 1B show a conventional keyswitch 10 used in laptop computers and palm-top computers respectively in a state before actuation and after actuation.
Referring to FIGS. 1A and 1B, the keyswitch 10 is provided on a support panel 14 that in turn carries thereon a key housing 15, wherein the keyswitch 10 includes a keytop 11 adapted for being actuated by the finger of an operator. The keytop 11 further includes a cylindrical sleeve guide 11a accepted in a corresponding sleeve guide 15a provided on the key housing 15, and the keytop 11 is guided along the sleeve guide 15a of the key housing 15 as it is actuated by the finger of operator as a result of engagement of the cylindrical sleeve guide 11a and the corresponding sleeve guide 15a. Further, the keyswitch 10 includes a membrane 13 at a bottom part thereof in intimate engagement with the support panel 14, wherein the membrane 13 includes therein a membrane switch 12, and the keytop 11 engages with the membrane via a deformable, elastic actuator 16.
Thus, upon actuation of the keytop 11 as indicated in FIG. 1B by a finger 19 of the operator, the keytop 11 is pressed down while being guided by the sleeve guide 15a of the housing 15 in a direction Z.sub.2 (FIG. 1A), and the elastic actuator 16 collapses as indicated in FIG. 1B. In response to such a deformation of the actuator 16, the membrane switch 12 is closed. Upon release of the keytop 11, on the other hand, the elastic actuator 16 resiliently restores the original state, and the keytop 11 is pushed upward in a direction Z.sub.1 while being guided also by the sleeve guide 15a. Thereby, the membrane switch 12 returns to an open state.
Such a conventional keyswitch 10, while having an advantageous feature of simple construction, has a problem in that the overall height of the keyswitch 10, designated by H.sub.1 in FIG 1A, cannot be reduced satisfactorily. It should be noted that the height H.sub.1 is given as a sum of a height H.sub.2 of a top surface 15b of the key housing 15 as measured from a bottom surface of the support panel 14, a height H.sub.3 of the sleeve guide 15a as measured from the top surface 15b of the key housing 15, a height H.sub.4 corresponding to the stroke of the keyswitch, and a thickness t.sub.1 of a keytop face plate 11b.
Generally, the sleeve guide 15a has to have a height of at least 3-4 mm in order to hold the keytop 11 stably. Thus, it is necessary to secure a height of 3-4 mm for the height H.sub.3. Because of this, it has been necessary to secure a height of about 11 mm for the overall height H.sub.1 of the keyswitch 10, while such an overall height H.sub.1 is too large for the keyboards for use in laptop computers and palm-top computers. In relation to above, it should be noted that a keytop of a keyswitch is generally required to have a press down stroke S (FIG. 1B) of about 3 mm in order for the operator to confirm the action of pressing down of the keytop based upon the sense of the finger. This means that one has to secure a height of at least about 3 mm for the height H.sub.4 in the keyswitch 10.
The conventional key switch of FIGS. 1A and 1B has another drawback in that the key switch is vulnerable to dust.
In order to guarantee a smooth pressing down of the keytop 11 even when the finger of the operator has missed the center of the keytop 11, the sleeve guides 11a and 15a are engaged to form a very small gap 17 therebetween. Thus, when a fine dust particle has entered such a small gap 17, the movement of the sleeve guide 11a in the axial direction as indicated by arrows Z.sub.1 and Z.sub.2 is resisted substantially. For example, there may occur a case in which the keytop 11 may not return to the original state after being pressed down in the direction Z.sub.2, even when the operator has released the keytop 11.